Remove the 'sb_mark_dirty()', 'sb_mark_clean()' and 'sb_is_dirty()' helperswhich are not used. I introduced them 2 years and the intention was to makeall file-systems use them in order to be able to optimize 'sync_supers()'.However, Al Viro vetoed my patches at the end and asked me to push superblockmanagement down to file-systems and get rid of the 's_dirt' flag completely,as well as kill 'sync_supers()' altogether. Thus, remove the helpers.